When a 18650 battery is charged and discharged, this is counted as one cycle. And the cycle life is determined by the difference in capacity of your cell taken from its first-use rating to its present rating. For example, if your cell started at 3000mAh, when the battery hold less than 80% (2400mAh), we say its cycle life is over.
Moreover, the recharge cycles vary and are limited. As the battery is reused, it degrades due to oxidation and electro-chemical degradation. Generally, the 18650 batteries have a typical cycle life of 300 to 500 (charge, discharge cycles). When in high-amp or high-drain situations, this can decrease substantially to 200 cycles. If you go over the maximum discharge current limit, it can radically decrease the cycle life. If you maintain the batteries well, some good quality batteries may achieve more than 500 cycles.
So how to know your 18650 is dying? There are some ways you can tell if your 18560 is nearing the end of its life, and it’s time to get new ones.
*The battery loses its charge much faster than normal. It loses its charge after a couple of days or even worse overnight.
*The battery gets overheating when charging or discharging, warmer than normal.
*Recharge time gets abnormally long.
*You have used the battery frequently over 2 to 3 years.
*The battery can hold less than 80% of its original capacity.
*Check if there is any cracking or deformation in the battery.
How does this apply to a phone? If you charge your phone every day, in three years that’s over 1000 charges. People have cell phones for well over 5 years on the original battery.
Also, there is no mention of age. I am sure an 18650 battery after say 10 years is not going to be in great shape even if never used.
Most people I know change phones every two years. Even like that, battery capacity is always the first thing to degrade. a 20% or 30% loss in capacity is easy to notice.
I have Samsung 30Q’s I bought in Dec 2018. They get charged once a day for use in a vape device. Still going strong. 2 1/2 yrs, Around 900 cycles give or take a few.
capacity goes down, internal resistance goes up
eventually you either won’t get good runtime anymore (low capacity) OR the voltage drops when you pull high current (high IR), so eventually “turbo mode” just won’t work or won’t be much brighter.
but at 80% capacity I don’t see any reason to throw away yet if it still can do high currents. it’s just a useful rating to know but whether the light lasts 90 or 72 minutes on high, I doubt most users would even notice.
I don’t think the internal resistance can get to a point where the heat from discharging at high current causes thermal runaway but while charging at high currents that certainly is a different matter. That’s why I’m opposed to charging phones with more than 15W, eventually internal resistance is going to rise and then you’ve got a poisonous thermite bomb! 100W at 3.7V is 27A!!!
I have chinesium-grade AAA NiMHs that sat in the packaging for a couple of years, they have 650 instead of claimed 1000mAh left (bogous to begin with), so run time is lower but they can still put out good current…
I have a bunch of 30Q’s that are over 4 yrs old. They have been cycled a lot. They have been used in both hi drain lights and vape mods. They will only represent about 2100 mah now and if used in my vape mod they will die in an hour. Fresh off the charger they will degrade to about 3.7V in a day UNUSED.
Any battery is subject to eventual degrading, but might depend on how cared for. My original battery is still functioning on my Honda Goldwing…a 2010 bought in 2011…Triked in 2014…ridden little but always kept on a optimate 4 or 6 and still fully charges and checks good. Ten years that battery has lasted….ten years. I also now keep an optimate on my cars battery, whch being disable sometimes is not ridden for a month. Same result battery lasts forever. I have found that li-ion lasts longest if charged well before it drops to the minimum and is charged on a high quality charger that does not overcharge.
I have XP era laptops that are still going strong. Maybe not like 10 years ago.
But have been through 1000s of charge cycles.
All those oldies run 18650s.
But I suspect laptop BMSs are designed to preserve battery longevity.
All the Best,
Jeff
Primarily, it’s heat. Room temperature ages them rapidly, hot climates worse. Secondarily, charge voltage and depth of discharge.
Batteries are typically rated 500 full discharges. Half discharge might get you as much total energy as 1000 full cycles.
I put my batteries in a sealed bag in the fridge. Lights that don’t have a designated convenience use go in too lol. Even the EGO tool batteries, but i just use trash bag on them.
I have a Toshiba laptop from 1995. Original battery. It will run 30 minutes after a full charge which takes like 5 hrs. The next day the battery is completely dead again.
This is interesting. I have read the BU guidelines and other anecdotal inferences, but in my limited experience have heard few actual instances of li-ion users religiously employing this strategy. Would like know if anyone can definitively demonstrate quantitative advantages of low temp storage, as opposed to storing at room temperatures over the typical lifespan of a casual deployment cell (e.g. discharged/ recharged 2-4 times a month or less). I know it’s a lot more complicated than just that considering SOC, cycling variances, etc., but if storage temperature is the most significant factor in preserving capacity over time, it would be neat to hear real time/ real world testimony.
Check battery university…not at home so not convenient to look for you. 40 f will be about as good at full voltage as room temp at 3.5-3.6v but battery chemistry may change things… They don’t specify. Storage voltage + low temp should be near no capacity loss, they didn’t specify self discharge though. My refrigerated batteries don’t self discharge much …ymmv ( like .1v in months)
Edit: theory behind it is that low temps slow chemical reactions (not stop, deer fat still changes taste in 3mo frozen for example)
There was a good study about four years ago but people say today’s batteries are improved. Unfortunately, no new studies are cited. The old study indicated problems from high discharge rates, fast charge rates, and charging to high voltages. Deep discharge cycles below 3.5V were a problem that seems to have been mitigated in new batteries. Storage temperature was less important for users who will not keep cells for many years. Panasonic 18650.
Cells stored at 3.7V for 15 years are thought to exhibit a capacity fade of 6% at 10C and not quite 10% at 25C (77F). Stored at 4.1V at 25C they are estimated to lose 16% capacity in 15 years.
It has more data than I care to assimilate, but some of it is worth reading.
From another thread:
docware wrote: The study is dated 19.4.2017, cells are Panasonic NCR18650PD. You can read the whole study here :
